Saturday, 10 March 2012

 The addressing system our computers and phones use to find each other on the Internet is undergoing its largest ever transformation.
We’ve nearly run out of Internet addresses in their original form, known as IPv4. ISPs, website owners, and technology companies are upgrading to the new format, IPv6, but the transition will take years. To manage the process in the meantime, some ISPs are introducing equipment on their networks to perform Large Scale Network Address Translation (also known as LSN).
Depending on how it’s used, LSN equipment could have discriminatory or anti-competitive effects – for example, a poorly configured LSN device could disrupt Skype calling or real-time gaming. To keep these disruptions to a minimum, the Broadband Internet Technical Advisory Group (BITAG) – a group of technical experts dedicated to building consensus about broadband network management – has released a series of recommendations.
LSN equipment allows a large number of IPv4 devices to share a single IPv4 address, helping broadband providers to get more out of the dwindling number of addresses they have. Users that share one address are each assigned a different set of communications “ports,” allowing the ISP to distinguish one user’s communications from another based on port number.
But the Internet was designed on the idea that each address, on its own, would identify a single device.
With multiple users sharing an address, a user can keep fewer “connections” open – the number of connections users can have open is equal to the number of ports they’ve been assigned. This has the potential to interrupt access to some applications, like peer-to-peer file-sharing programs or websites that use simultaneous connections to gather lots of content in one place. Inbound communications – receiving a VoIP call or a chat message, for example – can also be disrupted because it’s not always clear to the VoIP or chat provider which of the users sharing an address is the correct recipient.
And LSN can give website owners headaches since it’s not obvious to them that users are sharing addresses. For example, if two users sharing the same address visit the same website and one of them is running a spambot, both users might have their access to the site revoked.
Luckily, the potential for LSN equipment to disrupt the user experience can be reduced if ISPs, application providers, and technology companies take a few crucial steps. That’s where BITAG’s recommendations come in. To help avoid conflicts between broadband operators and applications or websites that might otherwise feel the impact of LSN, BITAG’s key recommendations include:
Transparency. ISPs should disclose the location and timing of their LSN deployments to help with troubleshooting, and they should provide means for application providers to contact them if problems arise.
Application support. There are a variety of features that can be built into LSN technology to help traffic from independent applications successfully travel from one side of an LSN device to the other. The IETF is developing best practices in this area that should be followed.
Improved user uniqueness. Many websites currently use IPv4 addresses to distinguish between end users. BITAG suggests additionally using port information to distinguish users who may be sharing an address through the same LSN device.

Rapid deployment of IPv6. The best way to reduce the impact of LSN is for IPv6 to become the dominant addressing scheme on the Internet. BITAG suggests that ISPs deploy IPv6, that equipment manufacturers support IPv6 in their devices, and that applications support IPv6 as soon as possible.
As we’ve written before, many stakeholders in the Internet community have long supported the idea that getting engineers together to discuss technical considerations relating to emerging network management practices can help create a more constructive debate about how Internet traffic is managed. BITAG’s recommendations for LSN are a thoughtful contribution on a topic that will continue to garner attention as the transition to IPv6 progresses.

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